It's doubtful you are sending the 4K display a 4K signal. So the problems of native resolution will show. Read https://www.google.com/search?q=native+lcd+resolution&ie=utf-8&oe=utf-8
While you seem to have found a temp fix, you need to call LG on this as most models are less than mature in the TV firmware.
I'm trying to use my LG 42UB820T 4k tv as a display for my pc (via HDMI), but I'm having trouble getting a good picture. I've verified that I'm getting 4:4:4 chroma using a test image, renamed the input to "PC", and turned off all the auto picture and sharpness functions, but the picture still isn't right.
It looks like the TV is applying some sort of sharpening filter to everything - the text is blocky and thick, and any images look overly sharp and almost posterized. Occasionally I've been able to make the TV jump into some other mode where the image looks great (usually by changing the input name back and forth between blu-ray and PC), but as soon as I switch the tv on and off again I'm back to the blocky text.
It's a bit hard to show in an image, but this first one is of the TV displaying a nice image:
and this is the bad image I get most of the time:
Notice the www in the URL is much blockier in the second image, and the g in google inbox has been separated into two characters. I'm thinking that some sort of sharpness or dynamic contrast algorithm is at work here, playing with the antialiasing?
I'm hoping that someone on here can tell me why I can sometimes get a nice picture out of it, and hopefully help me disable LG's image processing for good.
thanks in advance!!!